1. Field of the Invention
This disclosure relates to the field of laser warning systems. In particular, to laser warning systems for use on combat vehicles to detect illumination of the vehicle by a laser targeter.
2. Description of the Related Art
Almost since their discovery, lasers have been used by the military for the targeting of enemy vehicles for ordnance delivery. Lasers are used in many forms for their task at ordnance delivery. Lasers are used in rangefinders, in target designators, and in other applications for targeting the enemy. In use, some lasers are steady, while others are pulsed. Further, lasers can be used by all types of military resources from individual infantrymen, specialized targeting vehicles (such as those for forward observation), combat vehicles (such as tanks), and even by battleships or aircraft.
One common utilization of the laser is to act as a rangefinder. This type of arrangement is particularly common in conjunction with armored fighting vehicles such as tanks. In these cases, the target enemy tank is illuminated by a laser from the firing tank and the time it takes for the laser to project from the firer and return to the firer (having reflected off the target) provides for an extremely accurate indication of the distance of the target. The firing tank will then have the laser data fed into a processor or computer which will direct automated systems for the tank""s main gun to fire a shell at an appropriate elevation to hit the target. Rangefinders can also rapidly calculate the speed and direction that a target is moving in addition to its distance, allowing for the weapon system to compensate for that movement and increase the likelihood of hitting the target.
Rangefinders are particularly beneficial for determining the distance of objects at a long distance and, in addition to tanks, are used in numerous other applications on the battlefield. In another exemplary application, forward observers sighting for distant artillery can use laser rangefinders to determine the distance they are from an enemy target. This information can then be combined with location information of the forward observer, such as from global positioning system (GPS) data. The total data can then be relayed to the remote artillery batteries which, from their own known location, can extrapolate the position of the enemy, and the artillery weapons can be directed at the target.
Lasers can also be used as a target illuminator or designator. Generally in this role, the illumination is used to guide weapons that can seek the laser indicator""s illumination, as opposed to the laser being used to predict a fire path upon its own reflection. In particular, with illuminators or designators, the ordnance can detect the laser light reflecting from the target, and computers on-board the ordnance or weapon system direct the ordnance to hit the illuminated or designated target. Laser designators are regularly used with laser guided bombs and missiles.
The above systems are all generally referred to as laser xe2x80x9ctargetersxe2x80x9d as they allow for the improved targeting of a designated enemy through the use of a laser beam. In particular, they allow for ordnance (for example, a missile fired from an off-shore ship or an artillery round) to be directed at a particular target because that target has been xe2x80x9chitxe2x80x9d or illuminated with the laser. Regardless of the type of laser targeter that is being used, the danger to the target is clear. Being illuminated by a laser targeter generally implies that a weapon is being directed at you, and often the time from laser illumination to the time of ordnance impact is relatively short.
Common targets of laser targeters are objects of particular value. These can be armored fighting vehicles (particularly in armored combat situations), supply trucks, command vehicles, aircraft, watercraft, bunkers, factories, or other types of military targets. To try and combat the threat presented by laser systems, laser warning systems have been created which can be attached to a vehicle to warn its crew that they have been illuminated and need to respond to an imminent threat. The warning systems generally operate as threshold detectors. In particular, the detectors are always sampling the light illuminating the vehicle (generally within a particular spectrum where laser targeters are used) and when they receive a spike of illumination at a particular wavelength (a likely indication that a laser system has illuminated the target) which is larger than a threshold value, they provide a warning to the crew that they have probably been targeted by a laser targeter. The threshold is generally set high enough that changes in the ambient lighting or noise (e.g. because of sunlight changing during the day, or a nearby flashlight in the evening) are insufficient to set off the detector, while at the same time set sufficiently low that a laser targeter is detected whenever it is used to target the vehicle.
While these devices have gotten fairly good at detecting the presence of a laser, the limitation on these devices is that they can only provide warning of the presence of a laser. There is no indication of the actual position of the laser source. To put it more simply, these systems warn of a danger, while providing no indication of how to prevent the ordnance xe2x80x9cdirectedxe2x80x9d by the laser from hitting the target. Laser targeting systems can sometimes be avoided, such as, by taking certain sudden actions (such as radical movement) or by directing other ordnance upon the source of the laser to destroy it and have ordnance guided by the laser lose its navigation before it has locked onto the designated target. In some situations, knowledge of the source can allow for retaliation for the destruction of the target either by the target or by other units friendly to the target. In this way the damage which can be caused by an enemy with a targeting system can be minimized, or possibly prevented.
This minimization of damage is one of the most important in combat. Even if the target cannot avoid destruction, the inability of other forces friendly to the target to retaliate upon the laser source means that laser targeters essentially operate anonymously on the battlefield with little consequence of being active. Further they can target multiple enemy units before needing to avoid any retaliation. If the source of the laser could be rapidly identified, retaliatory fire could quickly be brought to bear to limit the effectiveness of the targeter (and to destroy it to prevent later use). Under such circumstances, the laser may not be used in the first place as the use of it may be overly dangerous, and/or strategically inefficient. Under the current system, however, a laser source is relatively safe from any retaliation, and can act without fear of being targeted for their targeting action.
What is missing in laser warning systems is the equivalent of what happens to another device in a parallel part of the spectrum, namely the radio frequency (RF) part. Radar could readily be used on the battlefield for rangefinding, designation, or any of the other tasks for which lasers are used. However, there exist electronic countermeasures for the use of radar. In particular, there have been developed interferometers to locate the source of the targeting radar such that the use of a radar on the battlefield will generally result in a retaliatory strike on the radar. Because of this, radar has lost effectiveness as a targeting apparatus in many circumstances to lasers because the single shot allowed by the radar prior to retaliation generally does not provide a sufficient battlefield advantage to justify the potential loss of the radar source.
The radar interferometer, however, cannot be readily adapted to detect the position of a laser. An interferometer for use at the frequencies of most laser light used in laser targeters would require a much closer tolerance and hence would be too expensive for battlefield use. There is therefore a need in the art for a laser warning system that can determine both the direction and distance to a laser source in an accurate manner that is suitable for use on a military vehicle under combat conditions.
Because of these and other previously unknown problems in the art, it is therefore desired to have a laser location system that allows for a user to determine the direction and/or distance to a source of light such as laser light. The system is designed to be functional under combat or other battlefield conditions and relatively simple and inexpensive to manufacture.
Described herein, amongst other things, is an embodiment of a laser warning device comprising: an array of at least two light detectors with each of the light detectors comprising a light sensor and a light control filter; wherein each of the light control filters comprises a plurality of microlouvers; and wherein the angle of the microlouvers in the first light control filter is different from the second light control filter. The microlouvers of one of the light control filters may be perpendicular to the plane and/or generally may be arranged 30xc2x0 from the perpendicular to the plane.
In an embodiment, the array comprises at least three light detectors the angle of the microlouvers in the third light control filter being different from the angles of the first and the second light control filters. In an embodiment, the microlouvers in the first light control filter are generally 30xc2x0 in one direction from the microlouvers in the second light control filter, which may be perpendicular to the plane of the array, and the microlouvers in the third light control filter may be generally 30xc2x0 in the opposite direction from the microlouvers in the second light control filter.
In another embodiment, there is described a laser warning device comprising: an arrangement of a plurality of arrays of light detectors, each of the arrays including at least two light detectors and each of the light detectors including a light sensor and a light control filter.
In still another embodiment at least one of the arrays may comprise at least three light detectors and/or may have a field of view of generally 60xc2x0. The arrangement of the arrays may be hexagonal and/or the plurality of arrays may comprise exactly six arrays. In another embodiment, each of the light control filters may comprise a plurality of microlouvers, wherein the angle of the microlouvers in a first light control filter is different from the angle of the microlouvers in a second light control filter.
In still another embodiment there is described a laser location system comprising: at least two laser warning devices wherein each of the laser warning devices includes at least two light detectors and wherein each of the light detectors includes a light sensor and a light control filter.
In a yet further embodiment, the laser warning devices in a laser location system may be a known distance apart and/or may comprise an arrangement of a plurality of arrays of light detectors, each of the arrays including at least two light detectors, and each of the light detectors including a light sensor and a light control filter. The plurality of arrays may comprise exactly six arrays, may be arranged hexagonally, and/or each of the light control filters may comprise a plurality of microlouvers, wherein the angle of the microlouvers in a first light control filter is different from the angle of the microlouvers in a second light control filter.
In a yet further embodiment, there is described a method of locating a light source comprising: providing a plurality of light detectors, each light detector comprising a light sensor and a light control filter comprising a plurality of microlouvers arranged at an angle to the plane of the light control filter; providing that the angle of the microlouvers in a first light detector be different from the angle in a second light detector, and that the angle of the microlouvers in a third light detector be different from the angle in a fourth light detector; arranging the first light detector and the second light detector into a first array, and arranging the third light detector and the fourth light detector into a second array; positioning the first array at a known distance and orientation relative to the second array; defining a predetermined point with a position known relative to at least one of the first array and the second array; receiving light from a light source at both the first array and the second array; determining the direction of the light source relative to both the first array and the second array; and calculating the distance of the light source from the predetermined point.